The present invention relates to a system for controlling the charging of a battery for an automotive engine.
A conventional charging system is shown in FIG. 5. The system comprises an alternator 9 having conduction coils 7, field coil 8, rectifier 6, and regulator 5. When an ignition switch 3 is turned on, current flows in a circuit consisting of a battery 1, switch 3, lamp 2, terminal L in a connector 4, field coil 8 and transistor T.sub.r2, thereby lighting up the lamp. On the other hand, transistors T.sub.r1 and Tr.sub.2 become conductive, so that the current flows in the coil 8. When the voltage at a terminal B for the battery becomes equal to the voltage at terminal L, the lamp 2 turns off. When the charging voltage at a terminal IG becomes higher than a set value, a zener diode 12 becomes conductive to turn on a transistor T.sub.r3. Thus, transistors T.sub.r1 and T.sub.r2 are turned off to de-energize the coil 8. Accordingly, the charging voltage decreases. Thus, the charging voltage is kept constant irrespective of amount of an electric load LD. In other words, even if the electric load is zero, the engine operates to rotate the rotor of the alternator to keep the set voltage. This means the loss of the output power of the engine and increase of fuel consumption.